Dynamic Routing Protocols part2

1. Dynamic Routing Protocols part2

2. CH2 Outline RIP OSPF

3. CH2 p3 Outline • Link State Routing Protocols • Link-State Routing Process • Advantages and disadvantages of link state routing protocols • OSPF Routing Protocol • Components of OSPF • OSPF Terminologies • OSPF Operation • OSPF Operational State • Dijkstra’s Algorithm

4. Types of Routing Protocols

5. Link-State Routing Protocols • In contrast to distance vector routing protocol operation, a router configured with a link-state routing protocol can create a complete view or topology of the network by gathering information from all of the other routers. • A link-state router uses the link-state information to createa topology map and to selectthe best path to all destination networks in the topology

6. Link-State Routing Process

7. Link and Link-State The first step in the link-state routing process is that each router learns about its own links, its own directly connected networks. 

8. Say Hello The second step in the link-state routing process is that each router is responsible for meeting its neighbors on directly connected networks.

9. Link State Updates The third step in the link-state routing process is that each router builds a link-state packet (LSP) containing the state of each directly connected link.

10. Flooding the LSP and Building the Link-State Database The fourth step in the link-state routing process is that each router floods the LSP to all neighbors, who then store all LSPs received in a database.

11. Computing the Best Path The final step in the link-state routing process is that each router uses the database to construct a complete map of the topology and computes the best path to each destination network.

12. Adding Routes to the Routing Table • The best paths are inserted into the routing table

13. Why Use Link-State Protocols? • Disadvantages compared to distance vector routing protocols: • Memory Requirements  • Processing Requirements  • Bandwidth Requirements

14. Protocols that Use Link-State • Only two link-state routing protocols: • Open Shortest Path First (OSPF) • most popular • two current versions • OSPFv2 - OSPF for IPv4 networks • OSPFv3 - OSPF for IPv6 networks • IS-IS • was designed by ISO • popular in provider networks

15. OSPF Routing Protocol

16. OSPF • OSPF is an IGP routing protocol. • It is a Link State routing Protocol based on SPF technology. • OSPF has fast convergence • OSPF supports VLSM and CIDR • Cisco’s OSPF metric is based on bandwidth • OSPF only sends out changes when they occur. • periodic updates (link-state refresh) every 30 minutes. • OSPF also uses the concept of areas to implement hierarchical routing

17. Link State Routing • In link state routing, each router shares its knowledge about its neighborhood with every router in the area. • The three features: • Sharing knowledge about the neighborhood. • Sharing with every other router. • Sharing when there is a change.

18. OSPF Routing Protocol

19. From CH2 p1 What are the components of OSPF?

20. Components of OSPF

21. Components of OSPF • OSPF Routers Exchange Packets • These packets are used to discover neighboring routers and also to exchange routing information to maintain accurate information about the network.

22. Components of OSPF • OSPF Routers run Dijkstra’s Algorithm to compute the best path to each destination network.

23. OSPF Routing Protocol • Link, Link State and LSDB. • Area. • OSPF Route Types • OSPF Routers Classifications. • OSPF Packets

24. Link and Link State • Link: Interface on a router • Link state: Description of an interface and of its relationship to its neighboring routers, including: • IP address/mask of the interface, • The type of network it is connected to • The routers connected to that network • The metric (cost) of that link The collection of all the link-states would form a link-state database (LSDB).

25. Networks Supported by OSPF • OSPF supports the following types of physical networks

26. Area • OSPF allows the grouping of routers into a set, called an area. • An area is a collection of networks, hosts, and routers all contained within an AS. • An AS can be divided into many different areas. • All networks inside area must be connected.

27. Area • Routers inside an area flood the area with routing information. • This technique minimizes the routing traffic required for the protocol.

28. Area • The topology of an area is hidden from the rest of the AS • Inside an area, each router has an identical LSDB. • Each area has its own copy of the topological database. • At the border of an area, special routers called area border routers summarize the information about the area and send it to other areas.

29. Area • Among the areas inside an AS is a special area called the backbone. • All the areas inside an AS must be connected to the backbone. • The routers inside the backbone are called the backbone routers. • Note that a backbone router can also be an area border router.

30. Area • Each area has an area identification. • The area identification of the backbone is zero.

31. Area • With multiarea, routing within the AS takes place on two levels, depending on whether the route to the destination lies entirely within an area (intra-area routing) or in another area (inter-area routing). • When a packet must be routed between two areas, the backbone is used.

32. OSPF Route Types

33. IR Area 3 Area 2 ABR/BR Area 0 ASBR To another AS OSPF Routers Classifications • OSPF routers can be classified into four overlapping types: • Internal routers, • Area Border routers, • Backbone routers, and • Autonomous system boundary routers

34. OSPF Routers Classifications

35. Types of OSPF Packets • OSPF routers exchange packets.

36. OSPF Routing Protocol

37. OSPF Operation • To maintain routing information, OSPF routers complete the following generic link-state routing process to reach a state of convergence 2 3 and 4 5 1

38. 1. Establish Neighbor Adjacencies • An OSPF-enabled router sends Hello packets out all OSPF-enabled interfaces to determine if neighbors are present on those links. • If a neighbor is present, the OSPF-enabled router attempts to establish a neighbor adjacency with that neighbor.

39. Establish Neighbor Adjacencies • OSPF creates adjacencies between neighboring routers. • The reason for forming adjacencies is to exchange topological information. • Not every router needs to become adjacent to every other router. • Adjacencies are established and maintained with hello packets. • These packets are sent periodically.

40. 2- Exchanging Link State Advertisements • LSAs contain the state and cost of each directly connected link. • Routers flood their LSAs to adjacent neighbors. • Adjacent neighbors receiving the LSA immediately flood the LSA to other directly connected neighbors, until all routers in the area have all LSAs.

41. 3. Build the Topology Table • After LSAs are received, OSPF-enabled routers build the topology table (LSDB) based on the received LSAs. • This database eventually holds all the information about the topology of the network.

42. 4. Execute the SPF Algorithm • Routers then execute the SPF algorithm that creates the SPF tree.

43. 5- Updating routing table • From the SPF tree, the best paths are inserted into the routing table.